Latensification of photographic images



Patented Oct. 11, 1949 Waldemar Vanselow and Raymond F, Quirk, Rochester, N. Y., assignors to Eastman Kodak 1 Company, Rochester, N

New Jersey Y., a A corporation of No Drawing. Application June 25, 1948,

Serial No. 35,296 1 9 Claims. (01. 95-88)] This invention relates to the latensification of photographic images, particularly by means of perborate compounds.

Various methods have been proposed for intensifying the latent image and effectively increasing the sensitivity and speed of photographic emulsions. These methods have included the use of chemical agents such as mercury vapor, peroxides, organic acids and sulfites. Some of these previously proposed methods have been objectionable for one reason or another and have not met with any notable commercial success partly because of the relative complexity of equipment or technique required and in certain cases because of the nuisance connected with using the latensifying agent in the manner proposed, but perhaps more because the results have not always been reproduceable nor as satisfactory as would be desired.

We have discovered a class of compounds, the alkali metal perborates, which possess superior properties as latensifiers for photographic images and which are devoid of many of the objections to previous latensifying agents. Therefore, one object of our invention is to provide perborate compounds which intensify photographic latent images. A further object is to provide the conditions under which the novel compounds are most effective as latensifying agents. Other objects will become apparent from the following de-' scription of our invention.

The objects of our invention are in general accomplished by treating a photographic emulsion layer, prior to development and subsequent to exposure, with a solution of an alkali metal perborate and then developing the latent image.

The perborate compounds comprising the preferred embodiment of our invention are the alkali metal perborates such as sodium or potassium perborate. These compounds may be used as latensifying agentsfor a variety of photographic silver halide emulsions under a wide variety of conditions but optimum results are obtained under controlled conditions of pH, concentration or in the presence of antifoggant compounds as will be seen from the following description of our invention.

. The mechanism by which the perborates intensify the latent image is not clearly understood; however, it is likely that the effect is 010-.

tainedas a resultof the deposition of silver ions" on existing sub-image centers. on the silver halide grains and the effect is more pronounced with the more sensitive grains as evidenced by a re-' duction in gamma. There is some evidence'that the fact that optimum results with perborates-as intensifiers are obtained under controlled conditions of pH, is connected with the oxidation-reduction behavior of solutions of the compounds.

That is, the perborates appear to exist in solution as an equilibrium of structureswhich is shifted by pH. High pH values'of theorder. of 10 seem to favor the true perborate ion and at lower pH values of the order of 8, a borate-peroxide structure may exist. Thisbehavior seems consistent with the observed effects of the perborates as latensifying agents. At pH values of from about 10 to 11, the perborate ion species appears to be responsible for the latensifying efiect and at pH values below 9, the borate-peroxide structure may be functioning, as a result of which appreciable fog is obtained when the compounds are used as latensifying-agents at this'range of pH. Thus at pH values of about'fi to 9, especially pH of about 6, it'is preferred to use an antifoggant such as 6-nitrobenzimidazole-nitrate together with the perborate compound in the latensifying solution in order to reduce fog. Therefore the range of pI-I'over which the compounds are most useful is from about 6 to 11, preferably aboutlO to 11- since the latter range represents the conditions under, which only negligible amounts of fog are obtained in absence of antifoggant compounds.

The concentration of the perborate compounds in the latensifying bath, as well as pH, should also be considered for optimum results. While concentration as well as pH will be found to vary somewhat -when optimum results are desired when using difierent emulsions and operating conditions, we find that concentrations of the order of about 2 to 10 grams of the perborate compound per liter of solution is satisfactory. However, as is shown in the following examples it is preferred with the fast emulsions of the negative type, such as the bromoiodide emulsions, to use about 10 grams of the compound per liter of intensifying solution, concentrations of the order of 50 grams per liter having been found to produce excessive fog in the absence of anti- ,foggant' compounds. When latensifying slower ing out our ir'iventiorf.

Errample 1 Samples of a fast bromoiodide- -negativetype et film were exposed in an Eastman type'ib'i'nterisity scale sensitometer for & second using a 500- watt light source. The exposed 'sa'mples firemen treated with latensification Baths": 0501 nofiiiai iripotassium bromide, containing 10 grams of so dium perborate per liter, adjusted to pH 6 and containing the amounts of fi-nitrdbfizifiiidazole nitrate antiioggant compound indicated in thetable following. The exposed samples (NOSrZ- fi) were treated with the bath for one minute, following which all exposedfsamples were developed f'g'f 9 fiiii'ijiiite's' atlzfifc. in a" deverepefof" the following? composition; 1

Water 2:42; z 2.7:"..- p-Methylaminophenol= sulfate- Hydroquinone Sodium -sulfite' (de Potassiumbromide Boraxi Bor'i'c acid v Data obtaiiied' f ifi 'tli renewing tab 6 the above" tests are shown The eifect of using perborate-in-the latensificationbath as well-"asthe effect oi varying concentrations of anti-foggant is -apparent from these exainp'fes: i 7

Samples" of a stander-"r passive fins emuisita were; espossa- 1a sefisitoinetlerin the manner"- for o'ife" minute td'latii'sify baths 0.131 normal in news uremic" cmitaiaifigagrams arseen-1hrpereerate'perlitefat a error e and contaming varying amounts of c rritrob'nziini'daiole The characteristics of the samples thus treated are tabulated in the following table:

30/E speed at Density 0.2 over fog ple No. Gms. Antifogg nt/Lit er Gamma F0 The efiect of using perborate as well as antifog'gant in the latensifying bath in connection with einulsioiiso'f'this type is apparent from these Our invention is subject to other variations. For example-,we have discovered that the latensifica-tion effectcan be obtained using baths of reduced concentrations of perborate if the photographic material is dried after latensification and fisrore develbpmem. Multiple treatments of the photographic material in the baths, drying betweeh treatments, produces further speed increases. However, it ordinarily suificient to treatthe exposed materialonly once in: the

latens-ifyingbath. V 4 h It will be apparent to thQse-skilled iii the art that, as in most photograph-ic-prdcesses, results" will vary somewhat depending: upon the-technique used, the emulsions-under consideration and other factors.- Therefore, it is to be understood that the disclosure herein isby way o'f' example and that We consideras included in cur" invention all modificatioiis'and equivalents falling; within the scope of theappended'claifn's.

. What 'We clainri's: V I V I 1. The method of intensifying. a latent image of air-photographic silver halide emulsion layer vi hicii which comprises treating said-emulsion layer,

subsequent toex'posure and prior to devempment; with-an: aqueous solution ofan alkali metal perbprate at-a pH-of from approximately 6 to 11, and developing the latent: image.-

3. Themethod of intensifyinga latent image of a photographic silver halide emulsion-layer which comprises treating said emulsion layer, subsequent-to exposure and prior to development, with anaqueous solution of an alkali metal perbor'ate' at a pH of from approximately1'0 to 11, and dcveloping the latentimage- 4 4. The method of intensifying. a latent image of aphotographic silver halide emulsion layer which comprises-treating said emulsion layer,- subsequent to exposure and. prior to-development, with anaqueous solution of an alkali metal perberate and-an antifoggant compound at pH ofrom about 6 to v9, and developing the latent image.

5. The method ofintensifying a later-1timage of a-photographic silver halide emulsion layer which comprises treating said emulsion layer", subsequent to exposure and prior to development, with an aqueous solution of sodium perborate and an anti'foggaiit' compound at pH of from about 6 to 9; and developing th latent '6. The method'of intensifying a latent image of a photographic silverhalid'e emulsion layer which comprises treating said emulsion layer, subs d quent to exposure and prior to development, with an aqueous solution of sodium perborate and potassium bromide at a pH of about 6, and developing the latent image.

'7. The method of intensifying a latent image of a photographic silver halide emulsion layer which comprises treating said emulsion layer, subsequent to exposure and prior to development, with an aqueous solution containing from about 2 to 10 grams of an alkali metal perborate per liter, and developing the latent image.

8. The method of intensifying a latent image of a photographic silver halide emulsion layer which comprises treating said emulsion layer, subsequent to exposure and prior to development, 15

No references cited. 

